Process for preparing erythromycin compound

ABSTRACT

The present invention is to provide a process for producing a 2′-O-acetyl-4″-formyl-8,9-anhydroerythromycin A 6,9-hemiketal compound 4, and it provide a process for producing an erythromycin compound which comprises reacting a formylating agent with a 2′-O-acetylerythromycin A compound 2 to obtain 2-′-O-acetyl-4″-O-formylerythromycin A compound 3, then, acting an acid on Compound 3 to subject to hemiketalation, and then adding an aqueous basic solution in an aqueous solution to precipitate Compound 4 as free crystals.

TECHNICAL FIELD

The present invention relates to a process for preparing an erythromycincompound.

BACKGROUND ART

Compound A (11-oxo-12-alkoxy-8,9-anhydroerythromycin A 6,9-hemiketal)which is an erythromycin compound represented by the formula:

-   -   wherein R′ represents a lower alkyl group, is a compound useful        as a synthetic raw material of a gastro-prokinetic agent (for        example, see        de(N-methyl)-11-deoxy-N-isopropyl-12-O-methyl-11-oxo-8,9-anhydroxyerythromycin        A 6,9-hemiacetal (GM-611), New Current 7(13), pp. 19-21, issued        on Jun. 10, 1996). A method for producing the erythromycin        compound has been already known. Of these, from erythromycin A        represented by the formula:        2′-O-acetylerythromycin A represented by the formula:        is obtained, and then, via 2′-O-acetyl-4″-O-formylerythromycin A        represented by the formula:        to produce 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A        6,9-hemiketal represented by the formula:        and finally the above-mentioned Compound A is obtaind as        disclosed in Japanese Provisional Patent Publication No.        100291/1997 (which corresponds to U.S. Pat. No. 5,959,088). In        this method, however,        11-O-formyl-2′-O-acetyl-4″-O-formylerythromycin A is by-produced        in the formylation step, and the by-product is then transformed        to a hemiketal form        11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A        6,9-hemiketal as a by-product. This by-product is extremely        difficultly separated from an objective product,        2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal,        so that there is a problem that the objective product can be        difficultly obtained with a high purity. Thus, this method is        not suitable for an industrial preparation method of a synthetic        raw material of medical product required for purity        specification or excellent quality.

To solve the above-mentioned problem, the present inventors have studiedextensively to obtain a method of recovering2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal which isa final objective product in a state of high purity with substantiallynot containing a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal). As a result, they have found that after hemiketalationby reacting an acid which is after formylation in which a formylatingagent is reacted with 2′-O-acetylerythromycin A compound, crystals areprecipitated by adding an aqueous basic solution in an aqueous solution,then, crystals containing2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal compoundwith high purity and substantially not containing a by-product can beobtained, whereby they have accomplished the present invention.

DISCLOSURE OF THE INVENTION

The present invention relates to a process for producing an erythromycincompound which is a 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal compound (Compound 4) represented by the formula (4):

-   -   wherein R¹ and R² each independently represent a lower alkyl        group,        which comprises reacting a 2′-O-acetylerythromycin A compound        (Compound 2) represented by the formula (2):    -   wherein R¹ and R² have the same meanings as defined above,        with a formylating agent to obtain a        2′-O-acetyl-4″-O-formylerythromycin A compound (Compound 3)        represented by the formula (3):    -   wherein R¹ and R² have the same meanings as defined above,        then, reacting Compound 3 with an acid to subject to        hemiketalation, and adding an aqueous basic solution in an        aqueous solution to precipitate Compound 4 as free crystals.

The present invention also relates to a process further containing, inthe above-mentioned process, a step of obtaining Compound 2 which is astarting compound by reacting an acetylating agent to the erythromycin Acompound (Compound 1) represented by the formula (1):

-   -   wherein R¹ and R² each independently represent a lower alkyl        group,        before reacting a formylating agent to Compound 2.

BEST MODE FOR CARRYING OUT THE INVENTION

The processes of the present invention mentioned above are showntogether by the following reaction scheme.

In the respective compounds to be used in the processes of the presentinvention, R¹ and R² each independently represent a lower alkyl group,and as the lower alkyl group, there may be specifically mentioned, forexample, a straight or branched alkyl group having 1 to 4 carbon atomssuch as a methyl group, an ethyl group, a n-propyl group, isopropylgroup, a n-butyl group, an isobutyl group, a sec-butyl group, atert-butyl group, etc., preferably a methyl group, an ethyl group, an-propyl group, isopropyl group. Above all, the case where R¹ and R² areeach a methyl group, and the case where R¹ is a methyl group and R² isan isopropyl group are preferably mentioned.

(A) Formylation Step

In the process of the present invention, a formylating agent is reactedwith the above-mentioned 2′-O-acetyl-erythromycin A compound (Compound2) to formylate the hydroxyl group at the 4″-position of Compound 2 togive Compound 3.

In the step of the formylation, as the formylating agent, an optionalreagent can be used so long as it is an agent capable of introducing aformyl group into a hydroxyl group, and there may be mentioned, forexample, a mixture of formic acid-acetic acid compound such as formicacid-acetic anhydride, sodium formate-acetyl chloride, etc., and1-formylimidazole. It is preferably used a mixture of formic acid-aceticacid compound, more preferably formic acid-acetic anhydride. Theseformylating agents may be used singly or in combination of two or morein admixture. Incidentally, a mixture of formic acid-acetic acidcompound may be used in the form of a mixture previously produced as amixture and added, or separately added and mixed in the reaction system.With regard to a mixing ratio of the formic acids and the acetic acidcompound at that time, optimum range may vary depending on the kinds ofthe formic acids and the acetic acid compound to be used, and forexample, when formic acid-acetic anhydride is used, acetic anhydride ispreferably used in an amount of about 0.5 to 1.0 mol based on 1 mol offormic acid, and when sodium formate-acetyl chloride is used, acetylchloride is preferably used in an amount of about 1.0 to 2.0 mol basedon 1 mol of sodium formate.

An amount of the above-mentioned formylating agent to be used ispreferably about 1 to 10-fold mol, more preferably about 2 to 7-foldmol, particularly preferably about 4 to 6-fold mol based on the amountof Compound 2.

The formylation step is desirably carried out in the presence of a baseto improve reaction rate. As the usable base, there may be preferablymentioned an organic base, for example, pyridines such as pyridine,4-dimethylamino-pyridine, etc.; tertiary amines such as triethylamine,etc.; secondary amines such as diethylamine, diisopropylamine,pyrrolidine, piperidine, morpholine, etc. It is particularly preferablyused pyridine. These bases may be used singly or in combination of twoor more in admixture.

An amount of the above-mentioned base to be used is preferably about 1.0to 5.0-fold mol, more preferably about 1.0 to 1.5-fold mol based on theamount of Compound 2. Incidentally, when Compound 2 is a compoundobtained by subjecting Compound 1 to acetylation in the presence of abase, and Compound 2 obtained by the step of the acetylation is appliedas such to the reaction of formylation, the reaction may be carried outby not adding a base any more.

The formylation is preferably carried out in the presence of a solvent.The solvent to be used and an amount thereof are not specificallylimited so long as it does not inhibit the reaction, and those which donot inhibit the reaction through all the steps of acetylation,formylation and hemiketalation can be suitably used. There may bementioned, for example, carboxylic acid esters such as ethyl acetate,etc.; ketones such as acetone, etc.; halogenated aliphatic hydrocarbonssuch as dichloromethane, chloroform, etc., preferably ethyl acetate,acetone, more preferably ethyl acetate can be used. These solvents maybe used singly or in combination of two or more in admixture.

An amount of the above-mentioned solvent can be optionally controlleddepending on uniformity of the reaction solution or stirrabilitythereof, preferably 1,000 to 5,000 ml, more preferably 2,200 to 4,400 mlbased on 1 mol of Compound 2. Incidentally, when Compound 2 is obtainedby acetylating Compound 1 in a solvent and Compound 2 obtained in thestep of the acetylation is applied as such to the reaction of theformylation, the reaction can be carried but in the same solvent to thatused in the acetylation as a matter of course.

The formylation can be carried out by a method in which, for example,Compound 2 (when formylation is carried out directly after theacetylation as such, the resulting product may not be isolated orpurified), a formylating agent, a base and a solvent are mixed under anatmosphere of an inert gas (for example, nitrogen, argon, helium, etc.),and reacted, and the like. A reaction temperature at that time ispreferably about −40 to 5° C., more preferably −20 to 0° C., and areaction pressure is not specifically limited. A reaction time ispreferably about 7 hours.

Compound 3 obtained by the formylation step of the present invention maybe applied to the next hemiketalation step by once isolating andpurifying with a general method such as distillation, recrystallization,column chromatography, etc. after completion of the reaction, but it ismore preferred to use Compound 3 without isolation and purification tocarry out the formylation step and the hemiketalation step continuouslyin view of reaction operation.

(B) Hemiketalation Step

In the hemiketalation, Compound 3 subjected to formylation in theprevious step is reacted with an acid whereby the hydroxyl group at the6-position and the keto group at the 9-position are subjected tohemiketalation to prepare Compound 4, and then, an aqueous basicsolution is added to the mixture in an aqueous solution to precipitateCompound 4 as crystals. According to this step, Compound 4 can beobtained as free crystals.

As the acid to be used in the hemiketalation, there may be preferablymentioned organic acid, for example, formic acid, acetic acid, propionicacid, etc., and formic acid can be particularly preferably used. Theseacids may be used singly or in combination of two or more kinds inadmixture. Incidentally, the reaction may be carried out without furtheradding an acid when Compound 2 used as a stating compound in theprevious formylation step is obtained by acetylating Compound 1 in thepresence of an acid, and the formylation and hemiketalation steps arecarried out continuously from the acetylation step, or when an acid suchas formic acid, etc. is used in the formylation step, and thehemiketalation step is carried out continuously from the formylationstep.

An amount of the above-mentioned acid is preferably about 2 to 100-foldmol, more preferably about 4 to 20-fold mol, particularly preferablyabout 5 to 15-fold mol based on the amount of Compound 3.

The hemiketalation is desirably carried out in the presence of asolvent, and the solvent to be used and an amount thereof are the samethose described in the previous formylation. Incidentally, when Compound2 used as a starting compound in the previous formylation step isobtained by acetylating Compound 1 in a solvent, and the formylation andhemiketalation are carried out continuously from the acetylation, orwhen a solvent is used in the formylation, and the hemiketalation iscarried out continuously from the formylation, it can be carried outwith the same solvent to those used in the acetylation or hemiketalationstep as a matter of course.

As the aqueous basic solution to be added to precipitate Compound 4 ascrystals after preparing Compound 4 by subjecting Compound 3 tohemiketalation with an acid, there may be preferably mentioned anaqueous basic solution of an inorganic base, for example, an aqueousalkali metal hydroxide solution such as an aqueous sodium hydroxidesolution, an aqueous potassium hydroxide solution, etc.; an aqueousalkaline earth metal hydroxide solution such as an aqueous calciumhydroxide solution, an aqueous magnesium hydroxide solution, etc.; anaqueous alkali metal carbonate solution such as an aqueous sodiumcarbonate solution, an aqueous potassium carbonate solution, etc.; anaqueous alkali metal hydrogen carbonate solution such as an aqueoussodium hydrogen carbonate solution, an aqueous potassium hydrogencarbonate solution, etc. It is preferably used an aqueous sodiumhydroxide solution, an aqueous potassium hydroxide solution, an aqueoussodium hydrogen carbonate solution, more preferably an aqueous sodiumhydroxide solution, and an aqueous sodium hydrogen carbonate solution.These aqueous basic solutions may be used singly or in combination oftwo or more kinds in admixture. Incidentally, the aqueous basic solutionmay be added as a previously and separately prepared solution, or waterand a base are separately added to prepare it in a reaction system. Aconcentration of the aqueous basic solution at that time is notspecifically limited, and is preferably about 0.1 to 10 mol/L, morepreferably about 1 to 7 mol/L.

An amount of the above-mentioned aqueous basic solution to be used isnot specifically limited so long as it can make a pH of the reactionsolution preferably about 6.5 to 10.0, more preferably about 7.0 to 9.0.

These hemiketalation and crystals-precipitating steps are carried out,for example, by mixing Compound 3 (which may not be isolated andpurified), an acid and a solvent preferably at about 0 to 60° C., morepreferably at about 20 to 50° C. for about 2 hours under an inert gasatmosphere (for example, nitrogen, argon, helium, etc.).

Thereafter, an aqueous basic solution is added so that a temperature ofthe reaction solution becomes preferably about −5 to 30° C., morepreferably about 0 to 20° C., whereby Compound 4 is precipitated as freecrystals. A reaction temperature and a reaction step at this step arenot specifically limited. Incidentally, before adding the aqueous basicsolution, the reaction solution is washed with water or an aqueoussolution of an inorganic salt, so that an amount of the aqueous basicsolution to be used may be lowered.

Compound 4 obtained by the above-mentioned hemi-ketalation step andprecipitated as crystals can be isolated and purified by washing withwater or an aqueous solution of an inorganic salt and drying, aftercompletion of the reaction and after filtration thereof, and by carryingout the following purification step successively, Compound 4 having ahigher purity can be obtained.

(C) Purification Step

In the purification step, Compound 4 obtained in the previoushemiketalation step and precipitated as crystals is dissolved in anorganic solvent, washed with water or an aqueous solution of aninorganic salt and concentrated, and then, the concentrated solution isstirred under stirring in a saturated hydrocarbon solvent torecrystallized the compound, so that Compound 4 having a higher puritycan be obtained.

As the organic solvent to be used in the purification step, it is notspecifically limited so long as it can dissolve Compound 4, and theremay be mentioned, for example, carboxylic acid esters such as ethylacetate, etc.; aromatic hydrocarbons such as toluene, xylene, etc.; andhalogenated aliphatic hydrocarbons such as methylene chloride, etc.,preferably ethyl acetate and methylene chloride, more preferably ethylacetate can be used.

An amount of the above-mentioned organic solvent is not specificallylimited so long as it is an amount sufficient to completely dissolveCompound 4, and it is preferably about 1,500 to 60,000 ml, preferablyabout 9,000 to 30,000 ml based on mol of Compound 4. When Compound 2obtained in the acetylation step of Compound 1 is applied as such to thereactions of formylation and the subsequent hemiketalation, it ispreferably about 1,000 to 30,000 ml, more preferably about 5,000 to15,000 ml based on 1 mol of Compound 1 used in the acetylation step.

In the purification step, as the aqueous solution of an inorganic saltto be used for washing a solution obtained by dissolving Compound 4 inan organic solvent, there may be preferably mentioned a neutral aqueoussolution of an inorganic salt, and, for example, an aqueous sodiumchloride solution, etc. may be used. Incidentally, a concentration ofthe aqueous solution of an inorganic salt is not specifically limited.

As the saturated hydrocarbon solvent which can be used for mixing with asolution of Compound 4 after washing as mentioned above and for stirringunder heating, there may be preferably mentioned a straight, branched orcyclic saturated hydrocarbons having 5 to 12 carbon atoms, for example,pentane, hexane, heptane, octane, nonane, decane (those mentioned aboveall include various kinds of isomers), cyclopentane, cyclohexane,cyclopentane, etc., preferably hexane and cyclohexane, more preferablyhexane may be used. These saturated hydrocarbon solvents may be usedsingly or in combination of two or more in admixture.

An amount of the above-mentioned saturated hydrocarbon solvent to beused is preferably about 900 to 38,000 ml, more preferably about 3,800to 13,000 ml based on 1 mol of Compound 4 to be purified. When Compound2 obtained in the acetylation step of Compound 1 is applied as such tothe reactions of formylation and the subsequent hemiketalation, it ispreferably about 500 to 20,000 ml, more preferably about 2,000 to 7,000ml based on 1 mol of Compound 1 used in the acetylation step.

In the purification step, purification is carried out by dissolvingCompound 4 which was obtained in the hemiketalation step andprecipitated as crystals by adding an aqueous basic solution, in theabove-mentioned organic solvent, washing with water or an aqueoussolution of an inorganic salt, and concentrating the same until a volumeof the solution becomes about 0.05 to 0.5-fold, and then, theconcentrated solution is mixed with a saturated hydrocarbon solvent andthe resulting solution is stirred preferably at about 35 to 100° C.,more preferably at about 50 to 80° C. for about 0.5 hour under heating,and the like to carry out recrystallization. Incidentally, crystals ofpurified Compound 4 with higher purity can be easily isolated, afterfiltration, by washing and drying.

(D) Acetylation Step

As mentioned above, the process of the present invention relates to aprocess for preparing a 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycinA 6,9-hemiketal compound (Compound 4) from a 2′-O-acetylerythromycin Acompound (Compound 2) which is an erythromycin A compound in which the2′-position is acetylated, and the Compound 2 can be obtained byreacting an acetylating agent to the erythromycin A compound(Compound 1) to acetylate the hydroxyl group at the 2′-position ofCompound 1. Accordingly, the present invention is also relates to aprocess which further contains a step of obtaining Compound 2 of theformula (2) by reacting an acetylating agent with the erythromycin Acompound (Compound 1) of the above-mentioned formula (1) before reactingthe formylating agent with Compound 2 in the above-mentioned process ofthe present invention.

As the acetylating agent to be used in the acetylation step, there maybe mentioned, for example, acetic anhydride; acetyl halide such asacetyl chloride, etc.; acetate such as sodium acetate;1-acetylimidazole, and the like, preferably acetic anhydride and acetylchloride, more preferably acetic anhydride can be used. Theseacetylating agent may be used singly or in combination of two or more inadmixture.

An amount of the above-mentioned acetylating agent is preferably about1.0 to 2.0-fold mol, more preferably about 1.0 to 1.5-fold mol,particularly preferably about 1.0 to 1.2-fold mol based on the amount ofCompound 1.

The acetylation step is desirably carried out in the presence of a baseto improve a reaction rate. As the base to be used, there may bepreferably mentioned an organic base, for example, pyridines such aspyridine, 4-dimethyl-aminopyridine, etc.; tertiary amines such astriethylamine, etc.; secondary amines such as diethylamine,diisopropylamine, pyrrolidine, piperidine, morpholine, etc., andparticularly preferably pyridine can be used. These bases may be usedsingly or in combination of two or more in admixture.

An amount of the above-mentioned base is preferably about 1.0 to5.0-fold mol, more preferably about 1.0 to 1.5-fold mol based on theamount of Compound 1.

The acetylation step is desirably carried out in the presence of asolvent. As the solvent which can be used, it is not specificallylimited so long as it does not inhibit the reaction, and preferablythose which do not inhibit the reactions in all the steps of theacetylation step, and the formylation step and hemiketalation stepcarried out subsequent thereto are preferably used. Such a solvent maybe mentioned, for example, carboxylic acid esters such as ethyl acetate,etc.; ketones such as acetone, etc.; halogenated aliphatic hydrocarbonssuch as dichloromethane, chloroform, etc., preferably ethyl acetate andacetone, more preferably ethyl acetate can be used. These solvents maybe used singly or in combination of two or more in admixture.

An amount of the above-mentioned solvent to be used can be optionallycontrolled depending on uniformity of the reaction solution orstirability of the same, and preferably about 1,000 to 5,000 ml, morepreferably about 2,200 to 4,400 ml based on 1 mol of Compound 1.

The acetylation step can be carried out, for example, in an atmosphereof an inert gas (for example, nitrogen, argon, helium, etc.), by mixingCompound 1, the acetylating agent, the base and the solvent and reactedthese, and the like. A reaction temperature at that time is preferablyabout 0 to 50° C., more preferably 10 to 30° C., a reaction time isabout one hour, and a reaction pressure is not specifically limited.

Compound 2 obtained by the acetylation step can be used in thesubsequent formylation step of the present invention after onceisolating and purifying it by a general method such as distillation,recrystallization, column chromatography, etc., after completion of thereaction. However, it is preferred to use Compound 2 without isolationand purification to carry out the acetylation step and the formylationstep successively in view of reaction operation.

As mentioned above, the process of the present invention relates to aprocess for precipitating the objective compound as higher purity freecrystals by adding an aqueous basic solution to the2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal compound(Compound 4) in an aqueous solution obtained by formylation andhemiketalation, which is starting from the 2′-O-acetyl-erythromycin Acompound (Compound 2) which is an erythromycin A compound in which the2′-position is acetylated. Among the steps of the process of the presentinvention, a process of isolating and purifying the compound which is toprecipitate the compound from an aqueous solution containing Compound 4as higher purity free crystals by adding an aqueous basic solution canbe made a part of the present invention. Accordingly, the presentinvention also relates to a process of isolating and purifying a2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal compoundrepresented by the formula (4):

-   -   wherein R¹ and R² each independently represent a lower alkyl        group,        which comprises adding a basic solution to an aqueous solution        containing the compound and impurities to precipitate the        compound from the aqueous solution as free crystals. According        to the present process, in addition to the        2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal        compound produced through a role of steps as mentioned above,        the 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A        6,9-hemiketal compound is selectively precipitated from a        reaction mixture containing various kinds of by-products which        are difficultly isolated to give higher purity crystals of the        compound.

Incidentally, the erythromycin A compound of the formula (1) to be usedfor obtaining the compound of the formula (2) which is used as astarting compound of the process of the present invention can beprepared according to the method disclosed in Japanese ProvisionalPatent Publication No. 100291/1997 (which corresponds to U.S. Pat. No.5,959,088), and a method known in this field of the art.

EXAMPLE

Next, the present invention is specifically explained by referring toExamples and Comparative examples, but the scope of the presentinvention is not limited by these.

Example 1

To a flask having an inner volume of 20,000 ml equipped with a stirringdevice, a thermometer and a dropping funnel were charged 1000 g (1.36mol) of erythromycin A (Compound 1, obtained according to the methoddisclosed in Japanese Provisional Patent Publication No. 100291/1997),167 g (1.64 mol) of acetic anhydride, 172 g (2.18 mol) of pyridine and4,000 ml of ethyl acetate, and the mixture was reacted at 20 to 30° C.for one hour. Thereafter, a mixture of 564 g (12.3 mol) of formic acidand 626 g (6.13 mol) of acetic anhydride was added to the above mixtureand reacted at −5° C. for 8 hours, at 10° C. for 3 hours, and at 50° C.for 2 hours.

After completion of the reaction, while maintaining a liquid temperatureof the reaction solution to 10° C., 3,000 ml of water, and 3730 ml (22.4mol) of a 6 mol/L aqueous sodium hydroxide solution were added to themixture in this order to adjust a pH of the reaction solution to 7.0 to7.5. Moreover, 30 g (0.36 mol) of sodium hydrogen carbonate was added tothe mixture to adjust a pH of the reaction solution to 7.4 to 7.7 andthe mixture was stirred at −5 to 15° C. for 2 hours to precipitate freecrystals. The obtained crystals were collected by filtration to obtain718 g of white crystals. When the crystals were analyzed by highperformance liquid chromatography (analytical condition 1), a purity ofthe objective 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal (Compound 4) was 97.4% (areal percentage). Incidentally,an existence ratio of Compound 4 and a by-product(11-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 98.6:1.4.

Subsequently, the above-mentioned white crystals were dissolved in11,110 ml of ethyl acetate, and then, washed with 1,100 g of a 15% byweight aqueous sodium chloride solution, the organic layer was taken outand dried over anhydrous magnesium sulfate. After filtration, themixture was concentrated under reduced pressure, the concentratedsolution and 6,800 ml of n-hexane were mixed, and the mixture wasstirred under reflux (67° C.) for 30 minutes, and after cooling to roomtemperature and adding 1,200 ml of ethyl acetate, further at 0 to 5° C.for one hour. The obtained crystal was filtered and dried to give 519 gof Compound 4 (Isolated yield based on Compound 1: 48%) as whitecrystals with a purity of 97.4% (areal percentage according to highperformance liquid chromatography, analytical condition 1).

Incidentally, physical properties of Compound 4 were as follows.

Melting point; 233 to 236° C.

¹H-NMR (CDCl₃, δ (ppm)); 0.89 (3H, t, J=7.3 Hz), 0.94 (3H, d, J=7.8 Hz),1.55 (3H, s), 2.05 (3H, s), 2.27 (6H, s), 3.36 (3H, s), 4.62 (1H, d,J=7.3 Hz), 4.86 (1H, dd, J=1.1, 2.4 Hz), 5.16 (1H, d, J=4.9 Hz), 8.20(1H, d, J=1.0 Hz)

Example 2

To a flask having an inner volume of 1,000 ml equipped with a stirringdevice, a thermometer and a dropping funnel were charged 50 g (68 mmol)of erythromycin A (Compound 1), 8.4 g (82 mmol) of acetic anhydride, 8.6g (110 mmol) of pyridine and 200 ml of ethyl acetate, and the mixturewas reacted at 20 to 30° C. for one hour. Thereafter, a mixture of 28.2g (610 mmol) of formic acid and 31.3 g (310 mmol) of acetic anhydridewas added to the resulting mixture and the thus obtained mixture wasreacted at −5° C. for 7 hours, at 10° C. for 14 hours, and at 50° C. for2 hours.

After completion of the reaction, while maintaining the liquidtemperature of the reaction solution to 10° C., 150 ml of water, and 184ml (1.1 mol) of a 6 mol/L aqueous sodium hydroxide solution were addedto the solution in this order to adjust a pH of the reaction solution to7.0 to 7.7. Moreover, 1.5 g (18 mmol) of sodium hydrogen carbonate wasadded to the mixture to adjust a pH of the reaction solution to 7.5 to8.6, and the mixture was stirred at −5 to 15° C. for 2 hours toprecipitate free crystals. The obtained crystals were collected byfiltration to obtain 28.9 g of white crystals. When the crystals wereanalyzed by high performance liquid chromatography (analytical condition1), a purity of the objective2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal(Compound 4) was 96.2% (areal percentage). Incidentally, an existenceratio of Compound 4 and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 98.2:1.8.

Example 3

To a flask having an inner volume of 1,000 ml equipped with a stirringdevice, a thermometer and a dropping funnel were charged 100 g (140mmol) of erythromycin A (Compound 1), 16.7 g (160 mmol) of aceticanhydride, 17.2 g (220 mmol) of pyridine and 400 ml of ethyl acetate,and the mixture was reacted at 20 to 30° C. for one hour. Thereafter, amixture of 56.4 g (1,230 mmol) of formic acid and 62.6 g (620 mmol) ofacetic anhydride was added to the above mixture, and the resultingmixture was reacted at −5 to 0° C. for 8 hours, at 10 to 15° C. for forone hour, and at 40 to 50° C. for 2 hours.

After completion of the reaction, the reaction mixture was divided intotwo portions (hereinafter referred to as Reaction mixture A and Reactionmixture B, respectively).

While maintaining a liquid temperature of Reaction mixture A to 10° C.,150 ml of water, and 182 ml (1.1 mol) of a 6 mol/L aqueous sodiumhydroxide solution were added to the mixture in this order to adjust apH of the reaction solution to 7.46. Moreover, 1.5 g (18 mmol) of sodiumhydrogen carbonate was added to the mixture to adjust a pH of thereaction solution to 7.8 to 8.1, and the mixture was stirred at −5 to15° C. for 3 hours to precipitate free crystals. The obtained crystalswere collected by filtration to obtain 33.8 g of white crystals. Whenthe crystals were analyzed by high performance liquid chromatography(analytical condition 1), a purity of the objective2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal(Compound 4) was 96.6% (areal percentage). Incidentally, an existenceratio of Compound 4 and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 98.4:1.6.

Subsequently, the above-mentioned white crystals were dissolved in 555ml of ethyl acetate, the solution was washed twice with each 50 ml of a15% by weight aqueous sodium chloride solution, and the organic layerwas taken out and dried over anhydrous magnesium sulfate. Afterfiltration, the mixture was concentrated under reduced pressure, theconcentrated solution and 340 ml of n-hexane were mixed, and theresulting mixture was stirred under reflux (67° C.) for 30 minutes, andafter cooling to room temperature and adding 60 ml of ethyl acetate,further at 0 to 5° C. for one hour. The obtained crystals were filteredand dried to give 26.0 g of Compound 4 (Isolated yield based on Compound1: 24%) as white crystals with a purity of 97.4% (areal percentageaccording to high performance liquid chromatography, analyticalcondition 1).

While maintaining a liquid temperature of Reaction mixture B to 10° C.,150 ml of water, and 180 ml (1.1 mol) of a 6 mol/L aqueous sodiumhydroxide solution were added to the mixture in this order to adjust apH of the reaction solution to 7.47. Moreover, 1.5 g (18 mmol) of sodiumhydrogen carbonate was added to the mixture to adjust a pH of thereaction solution to 7.5 to 8.0, and the mixture was stirred at −5 to 0°C. for one hour to precipitate free crystals. The obtained crystals werecollected by filtration to obtain 29.0 g of white crystals. When thecrystals were analyzed by high performance liquid chromatography(analytical condition 1), a purity of the objective2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal(Compound 4) was 96.9% (areal percentage). Incidentally, an existenceratio of Compound 4 and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 98.5:1.5.

Subsequently, the above-mentioned white crystals were dissolved in 555ml of ethyl acetate, the solution was washed twice with each 50 ml of a15% by weight aqueous sodium chloride solution, and the organic layerwas taken out and dried over anhydrous magnesium sulfate. Afterfiltration, the mixture was concentrated under reduced pressure, theconcentrated solution and 340 ml of n-hexane were mixed, and theresulting mixture was stirred under reflux (67° C.) for 30 minutes, andafter cooling to room temperature and adding 60 ml of ethyl acetate,further at 0 to 5° C. for one hour. The obtained crystals were filteredand dried to give 21.0 g of Compound 4 (Isolated yield based on Compound1: 20%) as white crystals with a purity of 97.9% (areal percentageaccording to high performance liquid chromatography, analyticalcondition 1).

Example 4

To a flask having an inner volume of 1,000 ml equipped with a stirringdevice, a thermometer and a dropping funnel were charged 100 g (140mmol) of erythromycin A (Compound 1), 16.7 g (160 mmol) of aceticanhydride, 17.2 g (220 mmol) of pyridine and 400 ml of ethyl acetate,and the mixture was reacted at 20 to 30° C. for one hour. Thereafter, amixture of 56.4 g (1230 mmol) of formic acid and 62.6 g (620 mmol) ofacetic anhydride was added to the above mixture, and the resultingmixture was stirred at −10 to 5° C. for 8.5 hours, at 11° C. for 14.5hours, and at 40 to 50° C. for 2 hours.

After completion of the reaction, the reaction mixture was divided intotwo portions (hereinafter referred to as Reaction mixture A and Reactionmixture B, respectively).

While maintaining a liquid temperature of Reaction mixture A to 10° C.,150 ml of water, and 183.5 ml (1.1 mol) of a 6 mol/L aqueous sodiumhydroxide solution were added to the mixture in this order to adjust apH of the reaction solution to 8.10. Moreover, 1.5 g (18 mmol) of sodiumhydrogen carbonate was added to the mixture to adjust a pH of thereaction solution to 8.3 to 8.4, and the mixture was stirred at −5 to15° C. for 2 hours to precipitate free crystals. The obtained crystalswere collected by filtration to obtain 33.8 g of white crystals. Whenthe crystals were analyzed by high performance liquid chromatography(analytical condition 1), a purity of the objective2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal(Compound 4) was 96.1% (areal percentage). Incidentally, an existenceratio of Compound 4 and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 98.1:1.9.

Subsequently, the above-mentioned white crystals were dissolved in 555ml of ethyl acetate, the solution was washed twice with each 100 ml of asaturated aqueous sodium chloride solution, and the organic layer wastaken out and dried over anhydrous magnesium sulfate. After filtration,the mixture was concentrated under reduced pressure, the concentratedsolution and 340 ml of n-hexane were mixed, and the resulting mixturewas stirred under reflux (67° C.) for 30 minutes, and after cooling toroom temperature and adding 340 ml of ethyl acetate, further at 0 to 5°C. for one hour. The obtained crystals were filtered and dried to give25.7 g of Compound 4 (Isolated yield based on Compound 1: 24%) as whitecrystals with a purity of 97.1% (areal percentage according to highperformance liquid chromatography, analytical condition 1).

While maintaining a liquid temperature of Reaction mixture B to 10° C.,150 ml of water, and 181.6 ml (1.1 mol) of a 6 mol/L aqueous sodiumhydroxide solution were added to the mixture in this order to adjust apH of the reaction solution to 7.08. Moreover, 1.5 g (18 mmol) of sodiumhydrogen carbonate was added to the mixture to adjust a pH of thereaction solution to 7.6 to 7.7, and the mixture was stirred at −5 to15° C. for 2 hours to precipitate free crystals. The obtained crystalswere collected by filtration to obtain 34.0 g of white crystals. Whenthe crystals were analyzed by high performance liquid chromatography(analytical condition 1), a purity of the objective2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal(Compound 4) was 96.3% (areal percentage). Incidentally, an existenceratio of Compound 4 and a by-product(11-O-formyl-2′-C-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 98.2:1.8.

Subsequently, the above-mentioned white crystals were dissolved in 555ml of ethyl acetate, the solution was washed twice with each 100 ml of asaturated aqueous sodium chloride solution, and the organic layer wastaken out and dried over anhydrous magnesium sulfate. After filtration,the mixture was concentrated under reduced pressure, the concentratedsolution and 340 ml of n-hexane were mixed, and the resulting mixturewas stirred under reflux (67° C.) for 30 minutes, and after cooling toroom temperature and adding 60 ml of ethyl acetate, further at 0 to 5°C. for one hour. The obtained crystals were filtered and dried to give26.1 g of Compound 4 (Isolated yield based on Compound 1: 24%) as whitecrystals with a purity of 97.3% (areal percentage according to highperformance liquid chromatography, analytical condition 1).

Example 5

To a flask having an inner volume of 10,000 ml equipped with a stirringdevice, a thermometer and a dropping funnel were charged 1,041 g (1.42mol) of erythromycin A (Compound 1), 174 g (1.70 mol) of aceticanhydride, 179 g (2.18 mol) of pyridine and 4,164 ml of ethyl acetate,and the mixture was reacted at 20 to 30° C. for one hour. Thereafter, amixture of 588 g (12.7 mol) of formic acid and 652 g (6.39 mol) ofacetic anhydride was added to the above mixture, and the resultingmixture was reacted at −5 to 0° C. for 9 hours, at 10 to 20° C. for 12hours, and at 40 to 50° C. for 3 hours.

After completion of the reaction, while maintaining a liquid temperatureof the reaction mixture to 30° C., the reaction mixture was washed with2,082 ml of a 3% by weight aqueous sodium chloride solution, and 2,082ml of a 10% by weight aqueous sodium chloride solution in this order,2,600 ml of water, 1,650 ml (12.4 mol) of a 7.5 mol/L aqueous sodiumhydroxide solution was added to the mixture in this order to adjust a pHof the reaction solution to 7.0 to 7.7. Moreover, 30 g (36 mmol) ofsodium hydrogen carbonate was added to the mixture to adjust a pH of thereaction solution to 7.8 to 8.2, and the resulting mixture was stirredat 0 to 10° C. for one hour to precipitate free crystals. The obtainedcrystals were collected by filtration to obtain 930 g of white crystals.When the crystals were analyzed by high performance liquidchromatography (analytical condition 1), a purity of the objective2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal(Compound 4) was 94.8% (areal percentage). Incidentally, an existenceratio of Compound 4 and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 98.3:1.7.

Subsequently, the above-mentioned white crystals was dissolved in 13,849ml of ethyl acetate, the solution was washed twice with each 1,250 g ofa saturated aqueous sodium chloride solution, and the organic layer wastaken out and dried over anhydrous magnesium sulfate. After filtration,the mixture was concentrated under reduced pressure, the concentratedsolution and 7,079 ml of n-hexane were mixed and the resulting mixturewas stirred under reflux (67° C.) for 30 minutes, and after cooling toroom temperature and adding 1,249 ml of ethyl acetate, further at 0 to5° C. for one hour. The obtained crystals were filtered and dried togive 592 g of Compound 4 (Isolated yield based on Compound 1: 53%) aswhite crystals with a purity of 97.3% (areal percentage according tohigh performance liquid chromatography, analytical condition 1).Reference example 1 (Synthesis of unpurified2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal(Compound 4)).

To a flask having an inner volume of 3,000 ml equipped with a stirringdevice, a thermometer and a dropping funnel where charged 300 g (409mmol) of erythromycin A (Compound 1), 50.4 g (494 mmol) of aceticanhydride, 51.8 g (655 mmol) of pyridine and 1,200 ml of ethyl acetate,and the mixture was reacted at 20 to 30° C. for one hour. Thereafter, amixture of 169.3 g (3.68 mol) of formic acid and 188.3 g (1.84 mol) ofacetic anhydride was added to the above mixture, and the resultingmixture was reacted at 0 to 5° C. for 3 hours, at 10 to 20° C. for 12hours, and at 40 to 50° C. for 3 hours.

After completion of the reaction, while maintaining a liquid temperatureof the reaction mixture to 20° C., 900 ml of water, and 1,125 ml (6.75mol) of a 6 mol/L aqueous sodium hydroxide solution were added to themixture in this order to adjust a pH of the reaction solution to 7.7.Moreover, 10 g (119 mmol) of sodium hydrogen carbonate was added to thereaction solution to adjust a pH of the same to 7.9 to precipitate freecrystals. The reaction solution was filtered to separate it to crystalsand a mother liquor. With respect to the mother liquor, after separatingthe aqueous layer, the organic layer was washed twice with each 615 mlof a saturated aqueous sodium chloride solution. Also, the crystals weredissolved in 3,330 ml of ethyl acetate, and the solution was washedtwice with each 615 ml of a saturated aqueous sodium chloride solution.The organic layer was taken out and combined with the above-mentionedmother liquor, and the mixture was dried over anhydrous magnesiumsulfate. After filtration, the filtrate was concentrated under reducedpressure, the concentrated solution and 2,055 ml of n-hexane were mixedand the resulting mixture was stirred under reflux (67° C.) for 30minutes, and after cooling to room temperature and adding 360 ml ofethyl acetate, further at 0 to 5 C for one hour. The obtained crystalswere filtered and dried to obtain 236 g of white crystals (Isolatedyield based on Compound 1: 73%). When the crystals were analyzed by highperformance liquid chromatography (analytical condition 1), a purity ofunpurified 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal (Compound 4) was a purity of 91.1% (areal percentage,analytical condition 1). Incidentally, an existence ratio of Compound 4and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 94.6:5.4.

Example 6

To a flask having an inner volume of 200 ml equipped with a stirringdevice, a thermometer and a dropping funnel were charged 8.0 g (10 mmol)of unpurified 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal (Compound 4) obtained in Reference example 1, 40 ml ofethyl acetate and 60 ml of water, and the mixture was stirred at 0 to10° C. To the mixture was added 0.56 g (12 mmol) formic acid at the sametemperature, and then, 6.5 ml (19.5 mmol) of a 3 mol/L aqueous sodiumhydroxide solution was added thereto to adjust a pH of the reactionsolution to 6.2 to 7.9. The mixture was stirred at 0 to 10° C. for onehour, and crystals were collected by filtration and dried to give 5.9 gof Compound 4 (Isolated yield based on unpurified Compound 4: 74%) aswhite crystals with a purity of 96.4% (areal percentage according tohigh performance liquid chromatography, analytical condition 1).Incidentally, an existence ratio of Compound 4 and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 98.5:1.5.

Example 7

To a flask having an inner volume of 200 ml equipped with a stirringdevice, a thermometer and a dropping funnel were charged 16.0 g (20mmol) of unpurified 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal (Compound 4) obtained in Reference example 1, 80 ml ofethyl acetate and 60 ml of water, and the mixture was stirred at 0 to10° C. To the mixture was added 1.12 g (24 mmol) of formic acid at thesame temperature, and then, 4.0 ml (24 mmol) of a 6 mol/L aqueous sodiumhydroxide solution was added thereto to adjust a pH of the reactionsolution to 9.4. The mixture was stirred at 0 to 10° C. for one hour,and crystals were collected by filtration and dried to give 10.0 g ofCompound 4 (Isolated yield based on unpurified Compound 4: 63%) as whitecrystals with a purity of 95.9% (areal percentage according to highperformance liquid chromatography, analytical condition 1).Incidentally, an existence ratio of Compound 4 and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 98.0:2.0.

Example 8

To a flask having an inner volume of 200 ml equipped with a stirringdevice, a thermometer and a dropping funnel were charged 12.0 g (20mmol) of unpurified 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal (Compound 4) obtained in Reference example 1, 60 ml ofethyl acetate and 90 ml of water, and the mixture was stirred at 0 to10° C. To the mixture were added 22.5 g (331 mmol) of sodium formate and2.46 g (53 mmol) of formic acid at the same temperature, and then, 15 ml(45 mmol) of a 3 mol/L aqueous sodium hydroxide solution was addedthereto to adjust a pH of the reaction solution to 7.7. The mixture wasstirred at 0 to 10° C. for one hour, and crystals were collected byfiltration and dried to give 8.8 g of Compound 4 (Isolated yield basedon unpurified Compound 4: 73%) as white crystals with a purity of 95.5%(areal percentage according to high performance liquid chromatography,analytical condition 1). Incidentally, an existence ratio of Compound 4and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 97.8:2.2.

Comparative Example 1

According to the method described in Japanese Provisional PatentPublication No. Hei. 9-100291,2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal(Compound 4) was prepared. To a flask having an inner volume of 300 mlequipped with a stirring device, a thermometer and a dropping funnelwere charged 20.44 g (27.8 mmol) of erythromycin A (Compound 1), 3.41 g(33.4-mmol) of acetic anhydride, 3.53 g (44.6 mmol) of pyridine and 82ml of ethyl acetate, and the mixture was reacted at 20 to 30° C. for onehour. Thereafter, while maintaining the reaction solution to 0° C., amixture of 11.54 g (251 mmol) of formic acid and 12.8 g (125 mmol) ofacetic anhydride was added to the mixture, and the resulting mixture wasreacted as such for 3 hours, and after allowing to stand at roomtemperature overnight, it was reacted at 40 to 50° C. for 2 hours.

After completion of the reaction, 123 ml of ethyl acetate was added tothe mixture, and the mixture was washed with 123 ml of ice-water. Theorganic layer was separated and neutralized by adding 123 ml (136 mmol)of a saturated aqueous sodium hydrogen carbonate solution and 14.0 g(167 mmol) of sodium hydrogen carbonate (pH=6.5).

The organic layer was again separated, washed three times with each 41ml of a saturated aqueous sodium chloride solution, 30 ml of ethylacetate was added to the organic layer, and further the organic layerwas washed with 41 ml of a saturated aqueous sodium chloride solution.The aqueous layer after neutralization was extracted with 70 ml of ethylacetate, and combined with the previous organic layer and the mixturewas dried over anhydrous magnesium sulfate. After filtration, thefiltrate was concentrated under reduced pressure, and the concentratedsolution and 139 ml of n-hexane were mixed. The mixture was stirredunder reflux (67° C.) for 30 minutes, and after cooling to roomtemperature and adding 25 ml of ethyl acetate, further at 0° C. for onehour. The obtained crystals were filtered and dried to give 15.55 g ofwhite crystals. When the crystals were analyzed by high performanceliquid chromatography (analytical condition 1), a purity of theobjective compound 2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal (Compound 4) was 87.0% (areal percentage). Incidentally,an existence ratio of Compound 4 and a by-product(11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A6,9-hemiketal) was 95.6:4.3.

Incidentally, when the resulting material was analyzed by highperformance liquid chromatography (an internal standard method,analytical condition 1) using crystals of Compound 4 obtained in Example1 as 100%, a content of Compound 4 in the above-mentioned crystals was80%.

Incidentally, analytical conditions of high performance liquidchromatography in the above-mentioned Examples, Reference examples andComparative examples are as follows.

Analytical Condition 1

-   Column: Kromasil KR100-5C18-   Column temperature: 30° C.-   Eluent: Acetonitrile/water/28% aqueous ammonia (=700/300/3-   (Volume ratio))-   Flow rate: 1.0 ml/min.-   Detection wavelength: 215 nm    Analytical condition 2-   Column: L-column ODS-   Column temperature: 25° C.-   Eluent: Acetonitrile/water/28% aqueous ammonia (=725/275/40-   (Volume ratio))-   Flow rate: 1.0 ml/min.-   Detection wavelength: 215 nm

UTILIZABILITY IN INDUSTRY

According to the present invention, starting from2′-O-acetylerythromycin a compound, a process for preparing anerythromycin compound industrially suitable which realizes obtaining a2′-O-acetyl-4″-O-formyl-8,9-anhydro-erythromycin A 6,9-hemiketalcompound (compound 4) having high purity and containing substantially noby-product (11-O-formyl-2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycinA 6,9-hemiketal) as crystals.

1. A process for producing an erythromycin compound which is a2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal compound4 represented by the formula (4):

wherein R¹ and R² each independently represent a lower alkyl group,which comprises reacting a 2′-O-acetylerythromycin A compound 2represented by the formula (2):

wherein R¹ and R² have the same meanings as defined above, with aformylating agent to obtain a 2′-O-acetyl-4″-O-formylerythromycin Acompound 3 represented by the formula (3):

wherein R¹ and R² have the same meanings as defined above, then,reacting Compound 3 with an acid to subject to hemiketalation, andadding an aqueous basic solution in an aqueous solution to precipitateCompound 4 as free crystals.
 2. The preparation process according toclaim 1, wherein the process further comprises a step of reacting anacetylating agent to the erythromycin A compound 1 represented by theformula (1):

wherein R¹ and R² each independently represent a lower alkyl group, toobtain Compound 2 before reacting the formylating agent with Compound 2in the process according to claim
 1. 3. The preparation processaccording to claim 2, wherein after reacting with the acetylating agent,the obtained Compound 2 is reacted with the formylating agentcontinuously without subjecting to isolation and purification hereof. 4.The preparation process according to any one of claims 1 to 3, whereinafter reacting with the formylating agent, the obtained Compound 3 issubjected to hemiketalation continuously without subjecting to isolationand purificaion thereof.
 5. The preparation process according to claim 1wherein after subjecting to hemiketalation, an aqueous basic solution isadded to a reaction mixture to make a pH of the reaction mixture to 6.5to 10.0.
 6. The preparation process according to claim 1 wherein R¹ andR² are each a methyl group.
 7. The preparation process according toclaim 1 wherein R¹ is a methyl group, and R² is an isopropyl group. 8.The preparation process according to claim 1 wherein the formylatingagent is selected from the group consisting of a mixture of formicacid-acetic acid compound and 1-formylimidazole.
 9. The preparationprocess according to claim 1 wherein the formylating agent is selectedfrom the group consisting of formic acid-acetic anhydride, sodiumformate-acetyl chloride and 1-formylimidazole.
 10. The preparationprocess according to claim 1 wherein the formylating agent is selectedfrom the group consisting of formic acid-acetic anhydride and sodiumformate-acetyl chloride.
 11. The preparation process according to claim2, wherein the acetylating agent is selected from the group consistingof an acetic anhydride, an acetyl halide, an acetate and1-acetylimidazole.
 12. The preparation process according to claim 2wherein the acetylating agent is selected from the group consisting ofacetic anhydride, acetyl chloride, sodium acetate and 1-acetylimidazole.13. The preparation process according to claim 2 wherein the acetylatingagent is selected from the group consisting of acetic anhydride andacetyl chloride.
 14. A process for isolating and purifying a2′-O-acetyl-4″-O-formyl-8,9-anhydroerythromycin A 6,9-hemiketal compoundrepresented by the formula (4):

wherein R¹ and R² each independently represent a lower alkyl group,wherein the preparation process comprises adding a basic solution to anaqueous solution containing the compound and impurities to precipitatethe compound from the aqueous solution as free crystals.